Process for producing polynosic fibers

ABSTRACT

IMPROVED POLYNOSIC FIBERS ARE OBTAINED BY EXTRUDING A VISCOSE INTO A COAGULATION BATH, STRETCHING THE RESULTANT FILAMENTS IN A SECOND BATH, TREATING THE STRETCHED FILAMENTS IN A THIRD BATH AND SUBJECTING THE FIBERS TO REGENERATION. SAID VISCOSE HAS A $-VALUE OF AT LEAST 50. SAID COAGULATION BATH CONTAINS SULFURIC ACID, 20 TO 250 G./L. OF SODIUM SULFATE AND MORE THAN 3 G./L. OF FORMALDEHYDE. SAID SECOND BATH IS KEPT AT ABOVE 60*C. AND THE FILAMENTS ARE STRETCHED THEREIN UNDER A TENSION OF AT LEAST 0.3 G./D. SAID THIRD BATH CONTAINS AN ALKALI METAL SALT, AND ALKALINE EARTH METAL SALT, AN AMMONIUM SALT OF SULFURIC ACID, OR A MIXTURE THEREOF AND IS KEPT AT A PH OF 2.0 TO 10.5 AND AT 40* TO 90*C. THUS PRODUCED POLYNOSIC FIBERS HAVE HIGH TENACITY, HIGH WET-MODULUS AND EXCELLENT FIBRILLATION RESISTANCE.

April 13, 1971 DYE EXHAUST/0N in Q g g 8 Q 8 M. KUBOTA E'I'AL 3,574,813

PROCESS FOR PRODUCING POLYNOSIC FIBERS Original Filed Sept. 22, 1967 F/GI/ CH 0 7.5 g/[ United States Patent 3,574,813 PROCESS FOR PRODUCING POLYNOSIC FIBERS Masaichi Kubota, Taro Yamamura, Atsushi Kawai, and Takehiro Katsuyama, Ohtake-shi, Masamichi lkeda, Iwakuni-shi, and Seiichi Omoto, Ohtake-shi, Japan, assignors to Mitsubishi Rayon Co., Ltd., Tokyo, Japan Original application Sept. 22, 1967, Ser. No. 669,800. Divided and this application Feb. 24, 1969, Ser. No. 801,317

Int. Cl. D01f 3/28 US. Cl. 264-497 6 Claims ABSTRACT OF THE DISCLOSURE Improved polynosic fibers are obtained by extruding a viscose into a coagulation bath, stretching the resultant filaments in a second bath, treating the stretched filaments in a third bath and subjecting the fibers to regeneration. Said viscose has a y-value of at least 50. Said coagulation bath contains sulfuric acid, 20 to 250 g./l. of sodium sulfate and more than 3 g./l. of formaldehyde. Said second bath is kept at above 60 C. and the filaments are stretched therein under a tension of at least 0.3 g./d. Said third bath contains an alkali metal salt, an alkaline earth metal salt, an ammonium salt of sulfuric acid, or a mixture thereof and is kept at a pH of 2.0 to 10.5 and at 40 to 90 C. Thus produced polynosic fibers have high tenacity, high wet-modulus and excellent fibrillation resistance.

This is a divisional application of US. Ser. No. 669,800 filed on Sept. 22, 1967.

The present invention relates to improved polynosic fibers and a process for producing the same.

'Recently, there have been proposed many processes for producing polynosic fibers excellent in properties by extruding a viscose having high v-value into a coagulation bath containing formaldehyde and stretching the resulting filaments in a hot dilute acid bath (second bath).

The filaments which have drawn from the coagulation bath containing formaldehyde have high stretchability, and therefore when they are highly stretched in the second bath kept at a high temperature, there are obtained fibers having high tenacity, high wet modulus and high resistance to water and alkali solution.

The above-mentioned processes are disclosed in, for example, United States Patent Nos. 2,937,070, 3,107,970 and 3,226,461, British Patent Nos. 910,878, 993,786 and 1,027,153, French Patent Nos. 1,266,492, 80,314/ 1,266,492, 1,302,294 and 1,351,736 and Belgian Patent Nos. 602,660, 608,811 and 626,075.

Generally, fibers obtained by extruding a viscose into a coagulation bath containing formaldehyde and highly stretching the resulting filaments in the second bath are inferior in fibrillation resistance, in particular.

In order to overcome such drawbacks, Belgian Patent No. 626,075 has proposed a process in which fibers are swelled by treatment with an aqueous alkali solution such as sodium hydroxide. This process, however, accompanies a lowering in tenacity of the fibers and is inefiective for the improvement in fibrillation resistance which is one of the important characteristics. Moreover, the process consumes in the swelling treatment a large amount of alkali solution and hence is not desirable fromthe economical standpoint, as well.

It has been found that in order to establish a method for improving fiber properties without causing any such drawbacks, it is extremely effective to adopt a process in which the filaments, obtained by extruding a viscose having a 'y-value of at least 50 into a coagulation bath containing sulfuric acid, sodium sulfate and formalde- 3,574,813 Patented Apr. 13, 1971 hyde and then stretching the resulting filaments in a second bath kept at above 60 C. under a tension of at least 0.3 g./d., are treated with an aqueous solution (third bath) containing an alkali metal salt of sulfuric acid, alkaline earth metal salt of sulfuric acid, ammonium salt of sulfuric acid or their mixture, said third aqueous bath being kept at a pH of 2.0 to 10.5 and at a temperature of 40 to 90 C. The third bath may be contained with a small amount of sulfuric acid salt of zinc or cadmium.

When the filaments, which have been prepared by extruding a high y-value viscose into a coagulation bath containing sulfuric acid, sodium sulfate and formaldehyde and then stretching the resulting filaments in a second bath, are introduced into an aqueous solution of, for example, sodium sulfate, the filaments unexpectedly swell to a great extent and, they are sometimes dissolved with the lapse of time. Such a phenomenon is observed not only in the case of sodium sulfate but also in the case of sulfuric acid salts of other alkali metals, alkaline earth metals or ammonium. Such swelling action is greatly affected by the pH and temperatures of the salt solutions employed. Therefore the pH and temperatures of the salt solutions to be used in the present invention should be within the ranges as described above. If the pH is less than 2.0, the difiusion of hydrogen ion into the fiber becomes marked, whereby the effective swelling of fiber due to the salt employed is restrained. On the other hand, if the pH is more than 10.5, the fiber is swelled to a great extent and is markedly lowered in tenacity. Moreover, even when, in the above case, a sulfuric acid salt of zinc or cadmium is incorporated into the salt solution, the specific action described hereinafter cannot be displayed. As to the temperature, it may be said that the higher the temperature, the stronger the swelling action of the salt. However, if the temperature is excessively high, regeneration of the fiber progresses to make difficult the swelling of the fiber. Preferable treatment temperature is within the range of 40 to 90 C. It has also been found that when an aqueous solution of a salt having a swelling action on fiber, as mentioned above, is incorporated with such a slight amount as less than 0.5 g./l. of a sulfuric acid salt of zinc or cadmium, the swelling of fiber is suitably controlled and the fiber properties are improved more effectively.

In practicing the present process on commercial scale, there is ordinarily used as a third bath an aqueous solution containing up to 50 g./l. of sodium sulfate and up to l g./l. of sulfuric acid. The third bath, however, is desirably incorporated, additionally, with up to 0.5 g./l. of zinc sulfate.

In the present invention, only fibers which are produced using :a coagulation bath containing formaldehyde can be treated with an aqueous salt solution, and the stretched filaments are still high in -value. From the above, it is interpreted that the swelling or dissolution of the fibers by action of said salts is ascribable to behaviors peculiar to cellulose hydroxymethyl-xanthate, which is a reaction product of cellulose xanthate and formaldehyde.

In the accompanying drawings, (FIG. 1 is a graph which well expresses the above relationship.

FIGS. 2 and 3 show the states of fibrillation of the present fibers and conventional fibers, respectively.

In FIG. 1, the horizontal axis is graduated with the sodium sulfate concentration in the third bath, while the vertical axis with the dye exhaustion as a characteristic represents the swelling effect. The solid line shows the case where a viscose containing 7% of cellulose and 4% of alkali and having a 'y-value of 80 and a viscosity of 260 poises is extruded into a coagulation bath containing 26 'g./l. of sulfuric acid, g./l. of sodium sulfate, 0.1 g./l.

of zinc sulfate and 7.5 g./l. of formaldehyde and kept at 25 C., and the resulting filaments are stretched to 380% in a second bath kept at 70 C. and are then treated in a third aqueous bath containing up to g./l. of sodium sulfate and 0.1 g./l. of zinc sulfate and kept at 70 C. The dotted line shows the case Where the treatments are effected under the same conditions as above except that no formaldehyde is contained in the coagulation bath and the stretch ratio in the second bath is 150%. From this graph, it is clear that no swelling effect is displayed at all in case the coagulation bath contains no formaldehyde.

Conditions for measuring the dye exhaustion are as follows:

Sample-3 g.

Japanol Brilla-nt Blue 6BKX0.3% (o.w.f.) Sodium sulfate-20% (o.w.f.)

Bath ratio-1 100 Temperature and time45 C. 20 minutes The absorbance of the residual liquid is measured by means of a photoelectric colorimeter to calculate the dye exhaustion.

When the present treating method is applied to filaments which have been stretched in the second bath under a tension of more than 0.3 g./d., the resulting fibers are improved not only in lateral properties of fiber, such as elongation, knot tenacity and the like, and in dyeability but also in fibrillation resistance.

The present process will be explained in more detail below.

The y-value of the viscose employed is required to be at least 50, preferably at least 65 (corresponding to a salt point of at least 16). If the y-value is lower than said effect, as well. The fibers which have been subjected to the salt treatment are then transferred to a high temperature acidic bath to complete regeneration.

If relatively strong swelling conditions are adopted in the above salt treatment, the cross-section of the fibers can be varied, and even hollow fibers can be obtained depending on the conditions.

The following examples illustrate the present invention:

EXAMPLE 1 A viscose containing 7% of cellulose and 4% of alkali and having a viscosity of 340 poises and a y-value of 83 was extruded into a coagulation bath containing 36 g./l. of sulfuric acid, 80 g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 7 g./1. of formaldehyde and kept at 25 C. The filaments withdrawn from the coagulation bath were immediately stretched to 450% the original length of the filaments under a tension of 1.2 g./d. in a second bath containing 1 g./l. of sulfuric acid and kept at 80 C. After cutting to staples, the fibers were treated for l minute in a third bath containing 0.1 g./l. of sulfuric acid, 10 g./l. of sodium sulfate and 0.1 g./l. of zinc sulfate and kept at 65 C. and a pH of 3.5. The 'y-value of the filamerits just before entering the third bath was 32. Subsequently, the regeneration of the fiber was completed in an aqueous bath containing 5 g./l. of sulfuric acid and kept at 75 C. Fiber properties of the thus obtained fibers are as shown in Table 1(A).

For comparison, fibers were produced in the same manner as above, except that the stretched filaments are cut to staples and then immediately subjected to regeneration without treating in the third bath. Fiber properties of these fibers are as shown in Table l-(B).

TABLE 1 Conditioned Wet Wet knot Dye tenacity elongation tenacity exhaustion Denier ((1.) {g.ld.) (percent) (g./d.) (percent) State of fibrillation A 1.3 5. 3 14 2. 5 84 As shown in Fig. 2. B 1.2- 5. 8 9 1.9 27 As shown in Fig. 3.

value, the filaments cannot be highly stretched in the second bath, with the result that not only no high tenacity fibers can be obtained but also the effect of the salt treatment cannot be sufficiently displayed.

The formaldehyde concentration of the coagulation bath is 3 to 15 g./l., preferably 3 to 10 g./l. It is desirable that the sulfuric acid concentration of the coagulation bath is within the range defined by the following equations:

Maximum concentration of sulfuric acid (g./l.)=8A+ 16 wherein A is the total alkali concentration in viscose which is preferably 2 to 8% The concentration of sodium sulfate is 20 to 250 g./l., and that of zinc sulfate, if it is to be incorporated, is desirably up to 0.3 g./l.

The filaments withdrawn from the coagulation bath are immediately stretched in the second bath to a high extent. In this case, the tension to be applied to the filaments should be at least 0.3 g./d. If the tension is smaller than 0.3 g./d., stretching becomes insuificient to make it impossible to obtain fibers having high tenacity. The second bath is desirably a low concentration sulfuric acid bath in view of the subsequent salt treatment. Further, temperature of the second bath should be at least 60 C. If the temperature is lower than said value, the filaments cannot be highly stretched, as well. The filaments stretched in the second bath are then treated in a relaxed state with an aqueous solution of the aforesaid salt. Treating temperature should be kept in the range of 40 to 90 C. If the temperature is below 40 0., little swelling effect can be attained, while if the temperature is above 90 C., regeneration of the fiber progresses to attain little swelling FIGS. 2 and 5 are photographs showing the state of fibrillation of fibers when the fibers cut into a length of 5 mm. were stirred for 10 minutes together with 10,000 times the amount of the fibers of water at 20 C., using a 320W home mixer rotating at 3,000 r.p.m.

EXAMPLE 2 The same viscose as in Example 1 was extruded into a coagulation bath containing 35 g./ 1. of sulfuric acid, g./l. of sodium sulfate, 0.2 g./l. of zinc sulfate and 8 g./l. of formaldehyde and kept at 25 C. The filaments withdrawn from the coagulation bath were immediately stretched to 410% the original length of the filaments under a tension of 1.1 g./ d. in a second bath containing 1 g./l. of sulfuric acid and kept at 75 C. After cutting to staples, the fibers were treated for 2 minutes in a third bath containing 5 g./l. of sodium sulfate and 0.1 g./l. of zinc sulfate and kept at 70 C. and at a pH of 7.0. The y-value of the filament just before entering the third bath was 39. Subsequently, the regeneration of the fibers were completed in a bath containing 5 g./l. of sulfuric acid and kept at C. Fiber properties of the thus obtained fibers are shown in Table 2(A) and about 10% of the fibers obtained were hollow.

For reference, fibers were produced in the same manner as above, except that the third bath contained no sulfates and was kept at 70 C. Fiber properties of these fibers are as shown in Table 2(B).

TABLE 2 Conditioned Wet Wet knot Dye tenacity elongation tenacity exhaustion Denier ((1.) (g./d.) percent (g./d.) percent We claim:

1. A process for producing improved polynosic fibers, characterized by extruding a viscose having a 'y-value of at least 50 into a coagulation bath containing sulfuric acid, 20 to 250 g./l. of sodium sulfate and more than 3 g./l. of formaldehyde, stretching the resulting filaments in a second bath kept at above 60 C. under a tension of more than 0.3 g./d., treating the stretched filaments in a third aqueous bath containing a salt selected from the group consisting of an alkali metal salt of sulfuric acid, an alkaline earth metal salt of sulfuric acid, an ammonium salt of sulfuric acid and their mixture, said third aqueous bath kept at a pH of 2.0 to 10.5 and at a temperature of 40 to 90 C. and then subjecting the fibers to regeneration.

2. A process according to claim- 1, wherein the third aqueous bath additionally contains up to 0.5 g./l. of a salt selected from the group consisting of zinc sulfate and cadmium sulfate.

3. A process according to claim 2, wherein the third aqueous bath additionally contains up to 1 g./l. of sulfuric acid.

4. A process according to claim 2, wherein the third aqueous bath contains up to g./l. of sodium sulfate and up to 0.5 g./l. of zinc sulfate.

5. A process according to claim 1, wherein a viscose containing 2 to 8% of alkali and having a salt point of at least 16 is extruded into a coagulation bath containing 3 to 10 g./l. of formaldehyde.

6. A process according to claim 1, wherein the coagulation bath contains sulfuric acid at a concentration defined by the following equations and up to 0.3 g./l. of zinc sulfate,

Minimum concentration of sulfuric acid (g./1.)=3A +8 Maximum concentration of sulfuric acid (g./l.) =8A+16 wherein A is alkali concentration (percent) in the viscose.

References Cited UNITED STATES PATENTS 2,515,889 7/1950 Nicoll 264-168 2,860,480 11/1958 Cox 264-197 3,107,970 10/ 1963 Kusunose et al. 264197UX 3,364,290 1/1968 Antema et al 264-197X 3,388,117 6/1968 Roberts et al 264197X 3,340,340 9/1967 Mytum 264-168 3,419,652 12/1968 Kubota et al. 264168 JAY H. WOO, Primary Examiner U.S. Cl. X.R. 

